Apr 20, 2017 1300 UTC Day 1 Convective Outlook
Updated: Thu Apr 20 12:55:03 UTC 2017 (20170420 1300Z Day 1 shapefile | 20170420 1300Z Day 1 KML)
Probabilistic to Categorical Outlook Conversion Table
Categorical Graphic
20170420 1300 UTC Day 1 Outlook Graphic
Day 1 Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
ENHANCED 11,477 5,956,536 Detroit, MI...Toledo, OH...Warren, MI...Sterling Heights, MI...Ann Arbor, MI...
SLIGHT 116,862 19,662,783 Indianapolis, IN...Columbus, OH...Oklahoma City, OK...Cleveland, OH...Cincinnati, OH...
MARGINAL 244,721 23,563,847 Tulsa, OK...St. Louis, MO...Pittsburgh, PA...Lexington-Fayette, KY...Louisville, KY...
Probabilistic Tornado Graphic
20170420 1300 UTC Day 1 Tornado Probabilities Graphic
Probability of a tornado within 25 miles of a point.
Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Day 1 Tornado Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
5 % 12,037 6,365,628 Detroit, MI...Toledo, OH...Warren, MI...Sterling Heights, MI...Flint, MI...
2 % 57,024 11,542,662 Cleveland, OH...Buffalo, NY...Fort Wayne, IN...Rochester, NY...Akron, OH...
Probabilistic Damaging Wind Graphic
20170420 1300 UTC Day 1 Damaging Wind Probabilities Graphic
Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point.
Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
Day 1 Wind Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
30 % 11,451 5,923,875 Detroit, MI...Toledo, OH...Warren, MI...Sterling Heights, MI...Ann Arbor, MI...
15 % 78,779 17,691,490 Indianapolis, IN...Columbus, OH...Cleveland, OH...Cincinnati, OH...Buffalo, NY...
5 % 254,883 25,120,178 Oklahoma City, OK...Tulsa, OK...St. Louis, MO...Pittsburgh, PA...Lexington-Fayette, KY...
Probabilistic Large Hail Graphic
20170420 1300 UTC Day 1 Large Hail Probabilities Graphic
Probability of hail 1" or larger within 25 miles of a point.
Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.
Day 1 Hail Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
15 % 93,172 17,091,514 Detroit, MI...Indianapolis, IN...Oklahoma City, OK...Cleveland, OH...Toledo, OH...
5 % 278,816 31,738,226 Columbus, OH...Tulsa, OK...St. Louis, MO...Pittsburgh, PA...Cincinnati, OH...
   SPC AC 201255

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0755 AM CDT Thu Apr 20 2017

   Valid 201300Z - 211200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS
   SOUTHEAST LOWER MI AND FAR NORTHEAST IN/NORTHWEST OH...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
   SOUTHERN GREAT LAKES AND OHIO VALLEY...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
   SOUTHERN PLAINS...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
   SOUTHERN HIGH PLAINS TO THE NORTHEAST STATES...

   ...SUMMARY...
   Severe storms capable of producing damaging winds, hail, and perhaps
   a tornado or two will be possible across parts of the southern Great
   Lakes region and Ohio Valley this afternoon and early evening.
   Isolated severe storms capable of producing large hail are also
   possible across parts of the southern Plains tonight.

   ...Great Lakes and Ohio Valley...
   The remnants of an MCS continue to move eastward across lower MI and
   far northern OH early this morning, with the somewhat stronger and
   more sustained convection occurring near a west/east-oriented warm
   front that parallels the IN/MI/OH border vicinity. An upstream upper
   trough over the Upper Midwest will continue eastward toward the
   Upper Great Lakes by this evening. A surface low over eastern IA
   early this morning may modestly deepen as the warm front spreads
   slowly northward across southern Lower MI and the Lake Erie
   vicinity. 

   Some concerns exist regarding the degree of destabilization later
   today ahead of the approaching cold front, particularly given
   observed mid/high-level cloud cover upstream, which is largely
   related to a weak eastward-moving impulse and convection over MO.
   Furthermore, near-frontal convergence should remain modest given the
   aforementioned impulse and tendency for a pre-cold-frontal veering
   of low-level winds. 

   Regardless, modest destabilization should occur this afternoon just
   ahead of the front with as much as 800-1200 J/kg MLCAPE expected
   around peak heating from IN into southeast lower MI and northwest
   OH. Strengthening west-southwesterly winds through a deep layer,
   with effective shear magnitudes reaching 35-40 kt late in the
   afternoon, could support both weak/short-duration supercells and
   eastward-moving clusters capable of damaging winds and some hail
   this afternoon and early evening. A tornado risk may exist as well,
   particularly across southeast lower MI and far northeast IN/far
   northwest OH in closer proximity to the surface low and warm front
   where low-level SRH will be maximized. 

   ...OK and northeast NM/TX panhandle...
   A southeastward-moving front is expected to decelerate and stall
   across OK and western north TX by this evening. Aided by nocturnally
   increasing isentropic ascent, storms should increase and intensify
   in a WSW/ENE-oriented corridor across OK this evening just north of
   the surface front. Ample shear through the cloud-bearing layer,
   along with relatively steep mid-level lapse rates and as much as
   1500-2000 J/kg of MUCAPE, will support elevated supercells capable
   of large hail.

   Farther west, while some spatial uncertainty exists regarding the
   stronger convection late tonight (especially given the highly
   elevated nature of the storms), various convection-allowing models
   support the development of potentially severe convection as far west
   as northeast NM late this evening and overnight. This would be
   supported by the gradual amplification of an upstream Rockies
   trough, with steepening mid-level lapse rates supported by a pocket
   of cooling mid-level temperatures. Severe hail appears possible late
   this evening and especially overnight across parts of northeast NM
   into the TX panhandle.

   ..Guyer/Jewell.. 04/20/2017

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